The present invention relates to an autonomous device of the kind which is arranged to automatically move on a work surface, such as a floor, removing dirt, such as gravel, sand, dust particles and the like, from said work surface. More specifically, the invention relates to such autonomous device which comprises a chassis provided with wheels and with a brush roller rotated by a drive motor during said movement for the purpose of brushing up the dirt towards a suction duct wherefrom, by means of a suction air stream, the dirt is conveyed to a dust container. The device also includes an electronic control device for controlling the drive motor of the brush roller.
An autonomous device as described above is often referred to as vacuum cleaner robot due to the fact that the device can automatically move around on a work surface, according to a predetermined pattern or by random changes of the direction of movement, cleaning the surface from loose dirt, such as gravel, sand, threads, hair and small particle dust. Most often, the autonomous device is battery-driven which means that it cannot have the same capacity as a common vacuum cleaner powered from the mains. Basically, a vacuum cleaner robot comprises a chassis with wheels for the movement and often one or more additional support wheels which are not driven. For the drive of the drive wheels often a separate motor is provided for each drive wheel. In addition, there is provided a unit for the collection of dust comprising a suction nozzle, a suction fan with drive motor and a dust container as well as connection conduits therebetween. Finally, an electronic control device is provided for the coordination of all activities of the vacuum cleaner robot and for the determination of patterns of movement. In addition, the control device is used for the determination of possible obstacles in the near surroundings of the vacuum cleaner robot so that a collision with obstacles is avoided and so that the robot can free itself if getting stuck in a corner or the like.
As a result of the limited suction capacity, suitably, a brush roller is provided which rotates during the movement of the device around the work surface brushing up dust particles towards a suction duct where the suction force takes over conveying the dust to the dust container. A suction force of any greater magnitude is not required at the work surface and the cleaning ability becomes reasonably good due to the joint action of the brush and the suction fan.
However, the rotating brush roller can give a problem when the surface consists of soft carpets provided with fringes. Upon movement of the device in over such a carpet the fringes can be brought with the brush to wind up on the roller and, in the worst case, to get stuck on the brush or between said brush and the adjacent brush roller housing. This can cause a problem with destroyed carpet fringes or cause damage to the brush roller or the accompanying drive motor.